Comparative research is being conducted on innate constraints on vocal learning. The only known animal model or the process of vocal learning underlying speech development in children is provided by birds. The P.I. and colleagues have shown that many avian sounds develop through a process of vocal learning, with numerous features in common with speech development. In further attempts to understand the details of the learning processes involved, and in the search for general laws that will include aspects of the human case as well, the role of auditory feedback in vocal development will be studied. Subjects will be two sparrow species known to engage in selective vocal learning. By temporal rearrangement of syllable components in computer-synthesized songs presented for vocal learning we will explore the nature of natural acoustic categories in vocal perception. Field studies with synthetic songs should elucidate the role of innate perceptual predispositions of their own vocal signals.